(1) Field of the Invention
The present invention relates to a method and apparatus for determining the resistance to scuff damage of a film on a panel. In particular, the present invention relates to a method and apparatus for determining and quantifying the resistance to scuff damage of paint or other films on various substrate materials including not only polymers (e.g. RIM-PU, TPO and composites) but also metals which uses an actuator to provide the correct pressure or load during testing. The actuator along with the computer controller enable the system to be repeatedly used with several different specimens or to conduct several tests on one specimen with consistent results.
The use of plastics has been increasing steadily in world auto industries driven mainly by energy savings movement. Numerous types of plastic materials are currently used for various applications. In bumpers and bumper fascias especially, there is considerable competition between reaction injection molded thermoset polyurethane (RIM-PU) and thermoplastic olefin (TPO). However, a major shift from RIM-PU to TPO is taking place for bumper fascias because of weight savings, cost effectiveness and recyclability (Mitra O'Malley and Joel Kopinsky, "Automotive Environmental and Safety Rules are Key Driving Forces for Innovation," Modern Plastics Encyclopedia` 94, pp. 20-22, Mid-November 1993). Based on extensive field studies by TPO manufacturers and their Original Equipment Manufacturer (OEM) partners, however, painted TPO automotive bumper fascias have experienced various dynamic contact induced paint damage during low-level auto to auto impact, door impact, and also, to a lesser extent, from standard projectile impact that occurs during normal driving conditions. The scuff damage of painted thermoplastic bumpers or fascias is a result of compression (indentation) and then subsequent sideways sliding while the two surfaces are still in contact. This damage occurs more readily at the higher temperature range of automotive service environment (i.e., 120.degree. F.-130.degree. F.), particularly for the softer substrates such as elastomer modified TPos. The bumper fascias consist of a plastic substrate with a surface treatment, a thermoplastic adhesion promoter, a primer paint and a top clear coat. Therefore, the coating-substrate structural integrity under dynamic contact exposures is not controlled by a single material or parameter. Recently; OEM's have tried to include the paint damage resistance in the performance specifications of a component as one of the engineering standards due to increasing customer complaints regarding the high paint damage susceptibility of plastic bumper fascias and body panels and the significant repair cost. No meaningful standard procedure is currently available due to the lack of general understanding of the problem and the complex structural composition of the component.
(2) Description of the Related Art
The related art has shown various apparatuses and systems for testing the surface damage resistance, such as scratch resistance of a film or sheet. Illustrative are U.S. Pat. No. 2,311,430 to Beno; U.S. Pat. No. 2,801,540 to Rondeau; U.S. Pat. No. 3,289,458 to Deichert et al; U.S. Pat. No. 4,791,807 to Oechsle and U.S. Pat. No. 5,490,410 to Markstrom.
In particular, U.S. Pat. No. 2,890,585 to Albrecht describes an apparatus for testing the hardness of a coating made of an electrically non-conducting material. The apparatus has an automatic shut-off upon failure or break through of the coating.
In addition, U.S. Pat. No. 3,087,326 to MacDonnell describes an apparatus for determining scuff resistance and/or surface breakdown of various materials by comparing the temperature variations between the contacting surfaces.
Also, U.S. Pat. No. 2,373,200 to Simmons et al describes an apparatus to test scratch adhesion of a panel which moves a stylus along the panel until the stylus penetrates the coating.
Also of interest are U.S. Pat. No. 3,985,026 to Griffin et al and U.S. Pat. No. 5,438,863 to Johnson. Griffin et al describes an apparatus for testing a surface coating on a glass container. The apparatus holds two glass containers and applies a load normal to the second glass container which is transmitted to the first glass container. The containers are then moved relative to each other. Johnson describes a portable testing system for determining material properties of an elastomeric material. The system uses a computer to process digital test data from the load cell of the test fixture and to control the overall test functioning of the system.
Several studies have been conducted on impact or chipping of painted plastic bumpers and bumper fascias. Illustrative are: Oosterbroek, M., and Boomgaard, R., Proceedings of the ACS Division of Polymeric Materials Science and Engineering, V. 58, Published by ACS, pp. 426-430, 1988; A. C. Ramamurthy, W. Isbell, V. Venditto and T. Jennings, SAE Tech Paper No. 932331, Dearborn, Mich. 1994; A. C. Ramamurthy, J. W. Holubka, and Dennis J. Mihora, "Adhesion Mechanics During Low-Speed Normal-Impact of Spherical "Rocks" into Multilayer Painted Steel Substrates," Proceedings of the 18th Annual Meeting of The Adhesion Society, pp. 52-55, 1995) and Gilmer, T. C. and Adesko, P. L., American Institute of Chemical Engineers, Workshop, V. 84, N 260, Published by AIChE, New York, pp. 16-32, 1988) (more relevant to a metal substrate). In addition, a few limited studies on the problems associated with compression-sliding type contact have also been conducted. Illustrative are: E. K. L. Lau, K. Swain, and S. Srinivasan, "Mar Resistance of Polyolefins: Mechanisms, Measurements and Materials," Proc. of The Third International Conference & Exhibit, TPOs in Automotive 1996, Oct. 28-30, 1996, Novi, Mich.; E. Eugene Shin, Charles K. Buehler, Preston W. Vallad, Roger Morgan, Lawrence Drzal, and Stephen M. Dwyer, "Reliability and Durability of Coated Composite Panels for Automotive Applications, "Proc. of The Third International Conference & Exhibit, TPOs in Automotive 1996, Oct. 28-30, 1996, Novi, Mich. and Michelle J. Mikulec and Thomas C. Yu, "Uppermost Stratum Morphology and Paintability of Thermoplastic Olefins", Proc. of The Third International Conference & Exhibit, TPOs in Automotive 1996, Oct. 28-30, 1996, Novi, Mich.
There remains the need for an apparatus and method for determining and quantifying the resistance to scuff damage of paint on a panel which allows for good reproducability and reliability and which uses an actuator to provide constant and accurate pressure.